TL;DR: RPC rate limiting is a mechanism that restricts how many requests your application can send to a blockchain node within a given time window. When you exceed the limit, subsequent requests are rejected (usually with an HTTP 429 error) until the window resets. Rate limits exist to protect shared infrastructure from abuse and ensure fair access across all users. Understanding and managing rate limits is essential for building reliable blockchain applications that do not break under load.
The Simple Explanation
Imagine a restaurant kitchen that can prepare 100 meals per hour. If 50 customers each order 3 dishes, the kitchen is at capacity. If one customer tries to order 50 dishes, the kitchen has to turn them away so that everyone else can still eat. Rate limiting works the same way. A blockchain node has finite processing capacity, and rate limits ensure that no single application monopolizes that capacity at the expense of everyone else using the same infrastructure.
When your application sends too many RPC requests too quickly, the node responds with an error instead of the data you requested. On most providers, this is an HTTP 429 "Too Many Requests" status code, often accompanied by a JSON-RPC error body that tells you how many requests are allowed, how many you attempted, and how long to wait before trying again. If your application ignores these signals and keeps sending requests, the provider may temporarily block your IP or API key entirely.
Rate limits are typically expressed as requests per second (RPS), requests per minute, or a combination of both. A provider might allow 25 RPS on a free tier, 300 RPS on a growth tier, and 1,000+ RPS on an enterprise tier. Some providers also apply per-method limits, meaning certain computationally expensive methods like debug_traceTransaction or eth_getLogs with large block ranges have lower individual limits than lightweight methods like eth_blockNumber.
Why Rate Limits Exist
Rate limits serve three primary purposes. First, they protect infrastructure stability. Blockchain nodes are stateful systems that maintain the entire blockchain's data and execute complex operations like EVM calls and state lookups. An unconstrained flood of requests can overwhelm a node's CPU, memory, disk I/O, or network bandwidth, degrading performance for all users or crashing the node entirely. Rate limits act as a circuit breaker that prevents any single client from causing cascading failures.
